Many different methods of scalability have been widely studied and standardized, including signal-to-noise ratio (SNR) scalability, spatial scalability, temporal scalability, and fine grain scalability, in scalability profiles of, e.g., the International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Moving Picture Experts Group-2 (MPEG-2) standard, and the ISO/IEC MPEG-4 Part 10/International Telecommunication Union, Telecommunication Sector (ITU-T) H.264 standard (hereinafter the “H.264 standard”). Most scalable video coding schemes achieve scalability at the cost of coding efficiency. It is thus desirable to improve coding efficiency while, at most, adding minor complexity. Most widely used techniques for spatial scalability and SNR scalability are inter-layer prediction techniques, including inter-layer intra texture prediction, inter-layer motion prediction and inter-layer residue prediction.
For spatial and SNR scalability, a large degree of inter-layer prediction is incorporated. Intra and inter macroblocks can be predicted using the corresponding signals of previous layers. Moreover, the motion description of each layer can be used for a prediction of the motion description for the following enhancement layers. These techniques fall into three categories: inter-layer intra texture prediction, inter-layer motion prediction, and inter-layer residue prediction.
In JSVM2.0, intra texture prediction using information from the previous layer is provided in the INTRA_BL macroblock mode, where the enhancement layer residue (the difference between the current macroblock (MB) and the (upsampled) base layer) is transformed and quantized. INTRA_BL mode is very efficient when the enhancement layer residue does not include too much edge information.
The following three possible configurations can be applied for the INTRA_BL macroblock mode: unrestricted inter-layer intra texture prediction; constrained inter-layer intra texture prediction; and constrained inter-layer texture prediction for single loop decoding.
Regarding the unrestricted inter-layer intra texture prediction configuration, the inter-layer intra texture prediction can be applied to any block without restrictions on the layer from which predictions are made. In this configuration, the decoder has to decode all lower spatial resolutions that are provided in the bitstream for the reconstruction of the target resolution.
Regarding the constrained inter-layer intra texture prediction configuration, the inter-layer intra texture prediction can be applied to macroblocks for which the corresponding blocks of the base layer are located inside intra-coded macroblocks. With this mode, the inverse MCTF is only required for the spatial layer that is actually decoded. For key pictures, multiple decoding loops are required.
Regarding the constrained inter-layer intra texture prediction configuration for single-loop decoding, the inter-layer intra texture prediction can be applied to macroblocks for which the corresponding blocks of the base layer are located inside intra-coded macroblocks for the MCTF as well as for key pictures. In this configuration, only a single decoding loop at the target spatial resolution is required.